1. Technical Field
An externally accessible switch device for securing and restricting access to data, configurations, parameters and other sensitive controls is disclosed. More specifically, a switch device for use with industrial control applications providing two or more magnetically actuatable non-contact switches capable of tamper detection is disclosed.
2. Description of the Related Art
Many process control devices require a switch to prevent users from re-programming or re-configuring a flow meter or scale. Such process control devices are used in the custody transfer of metered fluids which requires an agency sealable switch that keeps the user as well as the owner from modifying measurement, calibration, and calculation settings. Although the switches must be externally accessible, it is advantageous to use non-contact switches without through holes in the electronic enclosures. One advantage concerns the ingress protection that the enclosure provides against weather, dusts, and operator fingers. Sealing those things out makes for an electrically safer and more reliable product.
Other types of enclosures benefiting from the absence of through holes are those designed for use in a location where an explosion risk exits due to the presence of hazardous gases. These explosion-proof enclosures must contain an internal explosion resulting from an ignitable gas concentration coinciding with an internal electrical fault. The enclosure maintains safety by preventing a flame from exiting the enclosure and by resisting the resulting internal pressure wave. If a switch operator must pass through the enclosure, it must be certified for that use and for the expected gas hazards likely to be present.
An example of a currently existing design relies on a threaded shaft type of switch, manufactured by Adalet. This model XMOS carries an ATEX certificate and UL ratings for use with explosion-proof or flameproof enclosures. The shaft turns a selector switch inside the enclosure. However, these mechanical switches still do not provide a completely contact-free means of actuating. Other products such as Contrec and Isoil use brass bolts with magnetic heads installed from the exterior of an enclosure. These designs rely on explosion-proof construction and employ non-contact switch actuation as a simple means of maintaining the protective features of their enclosures. These magnetic switches, however, may be circumvented by external magnets. In particular, an unauthorized user with a sufficiently strong magnet can falsely actuate the magnetic switches and gain access to sensitive information without being detected.
Therefore, there is a need for an improved switch that can: operate from an exterior; be sensed from an interior; that minimizes agency costs associated with new product development and makes for better enclosure integrity. Specifically, there is a need for a non-contact magnetically actuatable switch capable of differentiating between authorized and unauthorized access.
While the following discussion will be directed toward non-contact tamperproof switches for industrial control applications, it will be noted that the devices disclosed herein are applicable to various fields beyond that of industrial control products and more generally can be applied to security devices utilizing magnetically actuatable switches.